I fully agree that the backlog should be part of the Kanban board. I don’t think it should be limited in numbers though. This, in my experience, is just not flexible enough in practise and the size of the backlog naturally changes. It’s the product managers job to clear out unimportant items as a way of prioritizing. We usually archive them, so they can still be found in search if something really pops up again later and turned out to be a wrong decision.
In terms of bug and issue tracking: I feel very strongly that bugs should be part of the regular Kanban board as well. If a bug is not important enough to not even make it into the Backlog, don’t even bother — youl’ll never get it done, because there’s always going to be something more important.
This system has worked pretty well for us over the past 2 years, even as we grew our teams, it’s been a very effective way to keep product development focussed.